1. Technical Field
The present invention relates to a working vehicle with an electromagnetic brake which has left and right wheels, a working machine, and left and right electromagnetic brakes provided corresponding to the left and right wheels.
2. Related Art
In the related art, ground working vehicles having working machines which are driven for ground work such as lawnmowing work and cultivating are known. In addition, in such ground working vehicles, electricity-driven ground working vehicles are considered having left and right wheels which are main drive wheels independently driven for travel by a motor such as an electric motor and a hydraulic motor, and steering wheels such as caster wheels.
For example, as a working vehicle, there exists a lawnmower vehicle equipped with a lawnmower which is a working machine, on which a worker rides for operations of traveling and lawnmowing, and which can travel by itself. Such a lawnmower vehicle is commonly called a riding type lawnmower vehicle. As the lawnmower, for example, there exists a lawnmowing rotary tool or the like. The riding type lawnmower vehicle is principally used off road, such as in a garden, and moves on the ground surface for the lawnmowing work.
For example, JP 2006-507789 A discloses a hybrid motive power unit equipped with an engine-generator integrated structure in which a rotor of a generator is connected to an engine shaft of an internal combustion engine. In a lawnmower exemplified as the motive power unit, electric motors are connected independently to a plurality of drive wheels and the drive wheels can be independently controlled with variable velocities so that starting, stopping, changing of a velocity, and changing of a direction of the lawnmower can be realized. As an example of turning by an independent change of the velocities of the drive wheels, a structure is described in which electric motors are connected to left and right rear wheels. As related art documents related to the present invention, in addition to JP 2006-507789 A, there exists JP H9-210106 A.
In the lawnmower vehicle in which left and right wheels are driven by left and right motors which are independent, as described in JP 2006-507789 A, a configuration may be considered in which left and right electromagnetic brakes are provided for braking the left and right wheels, to realize a working vehicle with an electromagnetic brake. In addition, in a working vehicle with an electromagnetic brake, a configuration may be considered which employs left and right electromagnetic brakes in which a brake releasing operation of the left and right wheels is executed by supplying electricity from a power supply and a brake operation of the left and right wheels is executed by cutting the supply of electricity from the power supply. Moreover, a configuration may be employed in which, in order to simultaneously brake the left and right wheels by the left and right electromagnetic brakes, a common switching unit is provided for the left and right electromagnetic brakes for switching the supply and cutting-off of the electricity between the left and right electromagnetic brakes and the power supply. However, there is a possibility that, when abnormality occurs in only one of the electromagnetic brakes, such as a case where the electricity is supplied to only the other the electromagnetic brake among the left and right electromagnetic brakes due to occurrence of abnormality in the circuits including the power supply and electromagnetic brakes, such as line disconnection, or occurrence of abnormality in the braking unit of one of the electromagnetic brakes among the left and right electromagnetic brakes when the electricity is to be supplied to the left and right electromagnetic brakes from the power supply, the vehicle turns in a manner not intended by the driver. For example, when one of the electromagnetic brakes is supplied with electricity from the power supply but the other electromagnetic brake is not supplied with electricity from the power supply, a difference may be caused in the traveling states of the left and right wheels. In this case, the vehicle may turn in some direction, and may move in a direction not intended by the driver. Because of this, there is a room for improvement in the point of effectively preventing the turn unintended by the driver even when abnormality occurs in one of the left and right electromagnetic brakes.
In consideration of this, JP H9-210106 A discloses an abnormality diagnosis device of a magnetic brake which is operated by a brake power supply circuit, which detects a current value supplied from the brake power supply circuit to a coil of the brake, extracts, from an amplified detected signal, a signal which allows understanding of an operation state of the brake, then compares the extracted value with a stored judgment value, and judges an operation deficiency of an armature of the brake. However, JP H9-210106 A only discloses a device which judges an operation deficiency of the armature, and does not disclose a unit which effectively prevents turning unintended by the driver even when abnormality occurs in one electromagnetic brake among the left and right electromagnetic brakes.
An advantage of the present invention is that in a working vehicle with electromagnetic brake, turning unintended by the driver is effectively prevented even when abnormality occurs in one electromagnetic brake among the left and right electromagnetic brakes.